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沿长江顺流而下,可以看到千山万谷,汹涌澎湃的三峡,也可以看到九曲回肠的荆江和潮平岸阔的江苏江段。在宜昌南津关,“山随平野尽,江入大荒流”(李白《渡荆门送别诗》)。长江就在这里由山区进入平原。一般说来,天然河流都可象长江一样,分为山区和平原两段。山区河流是水流改造山谷的产物。地壳运动,增加了河床演变的复杂性。山区河流具有下列特点:(1)河床纵比降大;(2)水流湍急紊乱;(3)山谷沿程宽窄不一,河道在平面上具有藕节状外形;
Down the Yangtze River, you can see thousands of mountains and valleys, the surging Three Gorges, you can also see the Jiuquhai Jingjiang River and tidal flat shore of Jiangsu section. In Yichang Nanjin Pass, “Mountain with the flat field to do, the river into the Great Recession” (Li Bai, “Ferry Gate to send poems”). Here the Yangtze River from the mountains into the plains. In general, the natural rivers can be divided into two parts: mountains and plains, just like the Yangtze River. Mountain river is the product of the river to transform the valley. Crustal movement increases the complexity of river bed evolution. The mountain river has the following characteristics: (1) the riverbed vertical ratio decreases; (2) the current turbulence is turbulent; (3) the width and width of the valleys along the valley are different; the river channel has a lotus root-like appearance in the plane;